The resulting 1,300-year cold spell coincides with the extinction of a host of massive mammals such as woolly mammoths, dire wolves, and sabertooths.

The Clovis culture, among the earliest humans in North America, may have suffered as well, according to Douglas Kennett, an archaeologist at the University of Oregon in Eugene, whose research appears in the current issue of the journal Science.

Kennett and colleagues found the layer of microscopic diamonds in sediments across North America that date to the start of the abrupt cooling.

The gems, the researchers argue, are consistent with a theory that Earth crossed a swarm of comets or carbon-rich meteorites that triggered cooling and die-offs.